The invention relates to a color television receiver having a first tuner for receiving a first video signal and a display for displaying the first video signal as first frames, each having two sequential fields of spaced scanning lines wherein the scanning lines in a second of the two fields are interlaced in the spaces between the lines in a first of the two fields. This color television receiver further includes a second tuner for receiving a second video signal, means coupled to the second tuner for subsampling the second video signal, and means coupled to the first tuner and the subsampling means for selectively applying the first video signal and the subsampled second video signal to the display. Arranged as such, the first video signal forms on the display the first frames while the subsampled second video signal simultaneously forms on the display second frames substantially smaller than the first frames and replacing a respectively-sized portion of the first frames.
Such a color television receiver is disclosed in U.S. Pat. No. 4,267,560 to Ishikawa et al in which three analog memories are used to store the luminance signal and the color difference signals, respectively, for three successive subsampling fields in the second video signal. It appears that it is necessary to store three successive subsampled fields of the second video signal in order to assure synchronization of the picture resulting from the subsampled second video signal with the picture resulting from the first video signal.
One of the limiting factors in providing consumers with digital television receivers is the cost for manufacturing large-scale memories. Hence, the prior art systems, which require at least one frame or, as in the above patent, one and one-half frames of memory, would be unduly expensive.